Interplanetary Planar Magnetic Structures

利用Sakigake太阳风资料和Yohkoh太阳软X射线图像，将行星际磁场矢量几乎沿平行于平面的所有方向的平面磁结构与太阳活动区的扩展进行了关联。在1993年1月至7月期间，我们在Yohkoh软X射线图象中发现了三个典型的具有Uchida等[1992]发现的活动区膨胀的平面磁结构，其中活动区日冕的环状结构以几公里/秒至几十公里/秒的速度反复向外膨胀。活动区的膨胀预计将在太阳质量损失中发挥重要作用。另一方面，并不是所有的活动区域都被观测到是行星际空间中的平面结构。在16次太阳源与活动区重合的Sakigake观测中，有9次观测结果显示出非螺旋磁场，包括平面结构、高离子密度或两者兼有，而其余7次（44%）与螺旋磁场的平均太阳风无显著差异，太阳风中的气压梯度被认为是平面磁场结构的一个可能原因。在5个没有整体速度梯度的Sakigake平面磁结构中，有2个处于压力梯度区域，而其他的则没有。高β等离子体的扁平的、缠绕的通量管（Crooker等人，1996）被重新检查以模拟平面磁性结构。为了再现平面磁结构，需要大量具有小螺旋度的磁通绳。场方向的变化主要是由于绳轴方向的变化，而不是由于每根绳中的场旋转。

Planar magnetic structures in which interplanetary magnetic field vector takes almost all directions that are parallel to a plane are correlated with EXPANDING ACTIVE REGIONS on the Sun by using Sakigake solar wind data and Yohkoh soft X-ray images of the Sun. During the period from January to July, 1993, we could identify three typical planar magnetic structures with the active region expansions found by Uchida et al. [1992] in the Yohkoh soft X-ray images, from which loop-like structures of active-region corona expand outward repeatedly at speeds of a few to a few tens of km/s even in the absence of any sizable flares. The active region expansions are expected to play an important role in mass loss from the Sun. On the other hand, not all the active regions were observed as planar structures in interplanetary space. In 16 Sakigake observations of solar wind plasma whose solar sources coincided with active regions, 9 had non-spiral magnetic field including planar structures, high ion density or both of them, but the other 7 (44%) exhibited no significant difference from average solar wind with spiral field.Pressure gradient in the solar wind is examined as a candidate cause of planar magnetic structures. In five of Sakigake planar magnetic structures with no bulk-speed gradient, two were in the regions of pressure gradient but the others were not. Flattened, intertwined flux tubes of high-beta plasma (Crooker et al., 1996) are re-examined to model planar magnetic structures. In order to reproduce a planar magnetic structure, a large number of flux ropes with small helicity are required. Variation of field direction is mainly due to variation of orientation of rope axs, rather than to field rotations in each of ropes.